DE2112271B2 - Process for processing used pickling liquid - Google Patents

Description

1/

untl22

(US-PS 36 26 755 and 8 22 89 258).

ShHcBHch it is known to detoxify cyani- \. to be carried out by means of oxidation. Chlorinated lime or Hypo-ISl is added to the ^{d! NoSd alkaline solution.} Any excess

Ee of active chlorine can be obtained by adding ^ ensulfate (pickling waste water) must be removed. This process concerns the oxidation in a sufficient aiii ! isch, presumably in an additional process step, the solution made more alkaline and icht the treatment of acidic wastewater, in which significantly different reaction results are to be expected

d. (W ei η er, "Die ^{Abwässer in der Metallindu S} trie" 1965, p. 178.) It is therefore the object of the present invention to create a method for processing used pickling liquid, with which the above-mentioned disadvantages can be avoided, in particular the disadvantages Pollution of waters can be avoided and all waste materials can be converted into usable products. The iron and steel works are to be put in a position to store the used pickling liquid in the vicinity of these works while avoiding contamination and health hazards and at the same time to supply usable products from it

obtain. ,,. ,,, ■

This task is carried out by a method of the introduction mentioned type, which is characterized in that sodium hypochlorite solution is used to precipitate the iron (III) hydroxide is added that the remaining after filtering off the iron-IU-hydroxide Solution is evaporated to dryness in order to obtain the sodium salt of the pickling acid that the during the reaction of the iron salt solution with the sodium hypochlorite, the chlorine gas with NaOH to form sodium hypochlorite is reacted and that the sodium hypochlorite obtained is recycled into the process will.

The main advantages of the present Verfahr.s are based on the fact that all components the used pickling liquid is processed into useful products or returned to the process cycle can be introduced. In addition, as a result of the liquid / liquid contact during the precipitation of the iron (III) hydroxide, no complex devices are required and the oxidizing agent used Sodium hypochlorite is cheap and widely available.

The method according to the invention can be seen in the flowchart.

The used pickling liquid is through the line 1 passed directly from the steelworks or from a collecting tank to a quenching or cooling tank 2. This container 2 is provided with means suitable for freezing or cooling and is usually double-walled and made of acid-resistant materia !. It can be provided with a jacket for heat exchange with the environment as small as possible. The temperature of the system is then lowered sufficiently that the iron salts crystallize out of the solution. If sulfuric acid is used for pickling, fall Iron sulfate crystals from the used pickling liquid. It should be noted that the optimal cooling temperatures, in which the desired iron salts crystallize out, from the special composition of the the used pickling solution. The separation of the solids from the liquid allows one Reuse of the acid, i.e. its return to the cycle. When using the invention Process, it is possible to recover 80% of the waste acid in its original strength, i.e. 15% acidity and to feed it back to the pickling process through line 4 without further treatment.

Any impurities, inhibitors, etc. contained in the spent pickling liquid, are mostly enclosed by the iron salt crystals. Then water, hot, cold or at room temperature, introduced through line 3 into container 4 to dissolve the crystals. The amount of water the amount required can vary greatly depending on the temperature. When hot water is available stands, an amount as small as half the weight of the crystals is sufficient to dissolve them quickly. It is advisable to filter the solution at this point in order to remove coloring substances, impurities, etc. remove. This can best be done by placing a filter on the bottom of the vessel 2 or in the for line 5 leading to the next vessel 6 is provided. Any suitable fluid, such as activated carbon, Glass fibers and the like are used; .. Mixtures of activated carbon and diatomaceous earth are also suitable. Activated charcoal is understood here to mean charcoal, which can perform the function of a filter medium. These and other commercially available filter media can be used, as can any of the im Commercially available filter devices, only it must be acid-resistant. There are many different filter devices obtainable, and their interpretation is not possible when using the method according to the invention critical. When the filtration is complete, the solids present in the liquid can and other impurities are fed to another cleaning system for processing.

The filtrate, which is obtained after filtration behind vessel 2, is returned through line 5. Reaction vessel 6, where it is brought into contact with NaOCl will.

Sodium hypochlorite. NaOCI is generally sold as a 4 to 5% aqueous solution. For example, the solution generally available contains 0.45 to 0.50 g of NaOCI per 100 ml of solution, which corresponds to 0.43 to 0.48 g of available chlorine. Any equipment that can effect liquid-liquid contact can be used for this purpose. However, the equipment must be gas-tight and chlorine-resistant. The reaction vessel 6 has openings at its upper end three, one to carry out the line 7 for introducing the NaOCl solution, a nrgic for Ch!, _A bführleuung 8 and for carrying out a stirrer. During the reaction that takes place in the chlorination vessel, the iron is converted into the trivalent state and a sodium salt is formed. The sodium salt. the result depends on the acid that was used for the pickling. The saturation of the iron (III) salt solution with NaOCI leads to the release of chlorine gas, which can be diverted or recovered in a known manner. The amount of NaOCI solution that is used is not critical. However, the amount should be sufficient to fill all of the iron in the solution. Apart from that, an excess of NaOCI would have practically no further effect and only unnecessarily increase the costs. After filtration, a pasty mass or sludge is obtained which is believed to be ferric hydroxide. In the form of a slurry, the remote hydroxide can be carried away through a suitable line 13. The mud

can ζ. B. conveyed to a furnace (not shown) and dried there to obtain ferric oxide, Fe2Ch will. A drying mechanism can also be built directly into the reaction vessel 6. if if desired, the ferric oxide can then be ground so that the end product has the desired grain size Has.

The filtrate from the reaction vessel 6 contains the salt, for example the sodium salt, which is formed during the chlorination became; it is in liquid or pasty form and can be converted into a conventional one through a suitable line Filtration device are passed in which the salt is isolated. The saline solution or slurry can can also be passed through line 10 to an evaporator 11 and that obtained there by evaporation dry salt can be removed through line 12 and used as a commercial product. Is the salt sodium sulfate, so it can z. B. be used as a drug, as a laxative or diuretic. Sodium sulfate is also used for dyeing and printing textiles, for setting colors, in cooling mixtures, in the manufacture of glass, in the manufacture of ultramarine pigments and in the paper industry. Any device suitable for this purpose can be used for the evaporation. For example, the Evaporator is a jacketed kettle that can be steam or electrically heated. He is either double-walled or provided with a heating coil between two walls.

The chlorine gas produced in the reaction is passed through line 8 to a chlorine recovery tank 9 in order to be possibly returned from there to the reaction vessel 6. The container 9 contains a NaOH solution. which reacts with the chlorine gas to form NaOCI.

The end products obtained in the process according to the invention are ferric oxide (Fe2O3), a sodium salt (usually sodium sulfate) and chlorine gas, which in turn is converted to sodium hypochlorite (NaOCl) will. This way there is no need to waste in lakes. To direct rivers or other bodies of water. It is also no need to bury large amounts of materials. All obtained in the process according to the invention Products are valuable materials and can be used for a variety of purposes will.

While the description primarily related to the pickling liquid used up during sulfuric acid pickling emerged, it should be pointed out again that the invention was also used up Pickling liquid refers to the use of hydrochloric acid or any other acid or mixture of acids arises

If the used pickling liquid is predominantly hydrochloric acid, the method according to the invention is shown in carried out in the same way with NaOCl, however, other products are produced. In the second stage, hydrochloric acid is used recovered in sufficient strength that it can be returned directly to the pickling process can be. Those in the crystallization stage, in containers The crystals obtained in 2 are iron chloride, which enters the reaction vessel through line 5 to the oxidation stage 6 is passed, in which NaOCl is introduced through line 7, which is with the ferric chloride with the formation of iron oxide, which is obtained in the form of a red paste. This paste is made through the pipe 13 removed from the vessel 6. The filtrate contains sodium chloride and is via line 10 in the Brought evaporator 11 to recover the sodium chloride. The sodium chloride gets through the pipe 12 removed from the evaporator. The chlorine gas that is released in the reaction vessel 6 is passed through the line 8 to the recovery unit 9, where it is treated with NaOH and, if desired, as NaOCI in the Reaction vessel 6 is returned.

If other acids are used as pickling liquids, the corresponding one is used in the cooling container 2

ίο Iron salt obtained, and in the evaporator 11 the corresponding sodium salt. In all cases the oxidation is carried out with NaOCl and the main steps of the process are identical.
In carrying out the process described herein, the spent pickling liquid can be at any suitable temperature. The used pickling liquid is expediently treated under normal conditions. In general, it is worked up as soon as it comes from pickling. Discontinuation or pretreatment is not required. Sodium hypochlorite is also added under normal conditions, i.e. environmental conditions. The sodium hypochlorite is usually added as an aqueous solution. Any suitable filtration device can be used to filter the ferric oxide produced in the process. The usual evaporation, filtration and drying devices can be used when carrying out the process according to the invention. The following example is intended to illustrate the particular characteristics of the present invention:

Spent pickling liquid based on sulfuric acid at room temperature, the finely divided solids and various impurities, such as other metal sulfates, metal sulfides, lubricants, inhibitors, hydrocarbons, Containing other organic compounds and the like was added to the double-walled crystallization vessel 2, which was provided with means for cooling and stirring. The temperature was then lowered to around 0 ° C to get the iron sulfate with most of the impurities and suspended solids crystallize out. Then they left to stand at this temperature for a while to avoid everything Let FeSO4 fail. After that, the content of the Vessel 2 filtered. The filtrate, which consisted essentially of a 15 percent sulfuric acid, was used for Pickling returned. Any suitable filter media can be used for this purpose After the filtrate was removed, the residue was dissolved in the gas-tight reactor with hot water tion vessel 6 pumped or otherwise conveyed for the oxidation reaction. Then the liquid, the Had normal conditions, saturated with NaOCl around da; To precipitate iron as a paste-like hydroxide. It was a sufficient amount of NaOCl was added until no more iron precipitated. It's been found that a volume ratio of NaOCI to consumed! Pickling liquid of 2: 1 is satisfactory if di < NaOCl solution is 5 percent. In order to ensure a sufficient «implementation, we stirred the solution« Iron was converted from the 2-valent to the 3-valent state and practically quantitatively out of the solution obtained as ferric hydroxide.

The chlorine gas released during the implementation came to be collected in cylinders, but was in these Example supplied to the container 9 and there saturated with sodium hydroxide solution and as a NaOCl solution for the reaction container 6 returned. The solids were durcl

ig m 8 H as

Filtration separated by an activated carbon filter, and that pasty Fe (OH) J brought to an oven and dried there. Drying was at one temperature carried out in the range from 200 to 700 "C. The dry Fc2O) was then ground in a ball mill.

The filtrate of the oxidation stage, one was fed to the evaporator 11, evaporated and the sodium sulfate. Glai was obtained from crystals. There could also be obtained by spray drying or their drying method

1 sheet of drawings

it i- : read

Claims (1)

Claim: Process for the processing of used heating liquid, in which the used pickling liquid is cooled to a sufficiently low temperature so that the iron salts contained in it largely crystallize out, the crystallized iron salts are separated from the supernatant liquid and dissolved in water from the obtained Iron salt solution iron (III) hydroxide is precipitated, the solution is filtered in order to separate the iron (III) hydroxide, and the separated iron (III) hydroxide is converted into Fe2O3 by heating, characterized in that for the precipitation of the iron (III) hydroxide Sodium hypochlorite solution is added so that the solution remaining after the iron-H-hydroxide has been filtered off is evaporated to dryness in order to obtain the sodium sac of the pickling acid, so that the chlorine gas released during the reaction of the iron salt solution with the sodium hypochlorite is converted with NaOH to sodium hypochlorite and that the sodium hypochlorite obtained it is recycled back into the process. The present invention relates to a method for processing used pickling liquid. To be more precise FAGT, the invention relates to Jm process for working up spent Beiiilüssipkeii in which the spent pickling liquid is up to a sufficiently tie fe temperature cooled so that crystallize in its contained iron salts to a large extent, the crystallized iron salts of the supernatant liquid, separated and dissolved in water, from the obtained iron salt solution iron (III) hydroxide is precipitated, the solution is filtered to separate the iron (III) hydroxide, and the separated iron ( III) hydroxide is converted into Fe2O3 by heating. The invention not only eliminates the problem of water pollution from used pickling liquid, moreover the used pickling liquids can be viewed as a source of versatile products. Pickling liquids are used to clean or pickle iron, steel and other metals in the form of sheet metal, rods, wire or other semi-finished products before they are processed into the finished object. For most purposes, dilute sulfuric acid is used. However, other acids such as hydrochloric acid, phosphoric acid, nitric acid, citric acid, mixtures of these acids, which can also contain hydrofluoric acid and the like, are used. Since the dawn of the modern steel industry , the removal of thin oxide layers that have formed on the metal surface has been effected by treating the surfaces with dilute solutions of the various acids prior to rolling or machining. In most cases, sulfuric acid is used. The reaction of sulfuric acid with the metal oxide that occurs during cleaning leads to the formation of a weak sulfuric acid solution of iron sulfate; this solution is commonly referred to as spent pickling liquid. If the pickling liquids contain hydrochloric acid, the used one is in the Ferric chloride fluid before. Large amounts of used pickling liquid are produced in the large steel and ironworks. Up to now it has been customary to remove the used pickling liquid from the plant area by simply channeling the solution into rivers, lakes or other bodies of water. However, this careless process is known to cause serious pollution problems. Where there are no natural bodies of water and where ίο the discharge of the used pickling liquid into natural water is prohibited, it was and is still customary to create large ponds near the iron and steel factories, into which the used pickling liquid is discharged and in which they are into the soil: i can seep away. On the one hand, however, the use of large areas of usable land for the processing of waste products is no longer justified and, on the other hand, such procedures are questionable, since the waste products can lead to pollution of the groundwater. In addition, British patent 8 87 975 already discloses a process for working up used pickling liquid known, in which the used pickling liquid to a sufficiently deep Temperature is cooled, so that the iron salts contained in it crystallize to a large extent, which crystallized out Iron brines are separated from the supernatant liquid and dissolved in water and from the iron salt solution obtained, iron (III) hydroxide is precipitated with sodium hydroxide solution and by oxidation with air will. However, this method has the disadvantage that the reaction to precipitate the iron (III) hydroxide takes place in two stages, the treatment being carried out in the second stage with a gaseous substance becomes what is known to be a more complicated device for carrying out the method than at requires a liquid substance. From US-PS 27 25 314 is also the oxidative work-up of metal treatment solutions, and Although cyanide-containing solutions, known with sodium hypochlorite. The US-PS 13 84 974 discloses a process for processing iron sulfate-containing pickling solution, in which this is mixed with a gaseous substance, such as NOj, as an oxidizing agent. The disadvantages caused by the gas-liquid contact also exist with this method, in particular the expensive equipment to achieve intimate mixing between the liquid and the gas : .. A method for regeneration goes from the OE-PS 2 44 7U7 hydrochloric iron solutions by roasting iron chlorides to iron oxides in the presence of Oxygen and water vapor emerge, in which the Clilor losses through discharge. Evaporation, etc., can be covered at least in part by the absorption of gaseous chlorine in the pickling solution or at some point in the kegeneration cycle with the oxidation of iron-II to iron-III chloride. Since that Working with chlorine as a gaseous substance not only has the disadvantages shown in connection with the methods described above, but also has If special precautionary measures are necessary, this method also has significant disadvantages on. Furthermore, the use of oxidizing agents such as H2O2 or hypochlorite solutions in the production of dyes based on iron oxide